Dispersion containing flame-resistant polymer, flame-resistant fiber, and carbon fiber

ABSTRACT

A dispersion contains a flame-resistant polymer, which can improve shaping stability of the flame-resistant polymer during ejection from a die orifice, and physical stability of a shaped product in a washing step. The dispersion containing a flame-resistant polymer is a dispersion in which a flame-resistant polymer is dispersed in an organic solvent, an in-water tensile strength thereof per unit cross-sectional area is 1.0 MPa or more and 6.5 MPa or less, the flame-resistant polymer can be preferably obtained by heat-treating an acrylonitrile polymer in the presence of at least one kind of acid, acid anhydride or acid chloride in an organic solvent, and a suitable organic solvent is a polar organic solvent.

RELATED APPLICATIONS

This is a §371 of International Application No. PCT/JP2007/074375, withan international filing date of Dec. 19, 2007 (WO 2009/078099 A1,published Jun. 25, 2009), the subject matter of which is incorporated byreference.

TECHNICAL FIELD

This disclosure relates to a dispersion containing a flame-resistantpolymer, and a flame-resistant fiber obtained by shaping the same, and acarbon fiber obtained by carbonizing the flame-resistant fiber.

BACKGROUND

Since a flame-resistant fiber is excellent in heat resistance and flameresistance, it is widely utilized, for example, in a spatter sheet forprotecting a human body from high-heat iron powder flying at weldingwork, or a welding spark and, further, in a flameproof heat insulatingmaterial of an aircraft, and a demand for the flame-resistant fiber inthose fields is increasing.

In addition, the flame-resistant fiber is also important as anintermediate raw material for obtaining a carbon fiber. The carbon fiberis widely used in various utilities, for example, aviation/spaceaeronautical materials such as aircrafts and rockets, and sports goodssuch as tennis rackets, golf shafts and fishing rods and further, isgoing to be used in transportation machinery utility fields of ships andautomobiles, because of excellent dynamical properties, various chemicalproperties and lightness. Furthermore, in recent years, application toelectronic instrument parts such as cases of mobile phones and personalcomputers, and electrode utilities of fuel cells is strongly demanded,because of high electrical conductivity and heat radiation properties ofthe carbon fiber.

The carbon fiber is generally obtained by heating a flame-resistantfiber at a high temperature in an inert gas such as nitrogen, andcarbonization-treating the fiber. Further, a conventionalflame-resistant fiber, for example, a polyacrylonitrile (PAN)flame-resistant fiber is obtained by subjecting a PAN precursor fiber toa flame-resisting reaction (cyclization reaction+oxidation reaction ofPAN) at a high temperature of 200 to 300° C. in an air. Thisflame-resisting reaction is an exothermal reaction, and is a reaction ina fiber form, that is, in a solid phase state. For this reason, longtime treatment is necessary for temperature control and, to completeflame-resisting in a desired time, it is necessary to limit a singlefiber fineness of the PAN precursor fiber to a small fineness of aspecified value or less. Thus, it cannot be said that the currentlyknown flame-resisting process is a sufficiently effective process.

As one method of solving the aforementioned technical problems,solutionization with a solvent was being studied. For example, thetechnique of heat-treating an acrylonitrile polymer powder in an inertatmosphere until the density is 1.20 g/cm³ or more, dissolving it in asolvent to fiberize it, and heat-treating the resulting fibrous materialhas been proposed (see JP-B No. 63-14093). However, since this proposaluses an acrylonitrile polymer powder, a flame-resisting reaction ofwhich has not proceeded, there is a problem that change in a viscosityof the solution with time is great, and yarn breaking easily occursfrequently. In addition, since as a solvent, a strongly acidic solventsuch as sulfuric acid and nitric acid which easily discomposes a generalorganic polymer is used, it is necessary to use an apparatus of aspecial material having anti-corrosion, being not practical from a viewpoint of a cost.

In addition, a method of mixing a heat-treated acrylonitrile-basepolymer powder and a not heat-treated acrylonitrile polymer powder todissolve the mixture in an acidic solvent similarly has been proposed(see JP-B No. 62-57723), but a problem of impartation of anti-corrosionto the apparatus, and instability of a solution remained unsolved.

Further, a method of heat-treating a solution of polyacrylonitrile indimethylformamide to convert polyacrylonitrile into a polymer with acyclized structure has been proposed (see Polymer Science (USSR), 1968,Vol. 10, pp 1537-1542). However, in this proposal, since a polymerconcentration is 0.5%, being a dilute solution, and a viscosity is toolow, shaping and molding into a substantial fiber are difficult and,when one tries to increase the concentration, a polymer is precipitated,and use as a solution was impossible.

In addition, a solution obtained by modifying polyacrylonitrile with aprimary amine has been proposed (see Journal of Polymer Science: Part A:Polymer Chemistry, 1990, Vol. 28, pp 1623-1636), but this solutionimparts hydrophilicity to polyacrylonitrile itself, flame-resisting ofwhich has not progressed, and technical idea is entirely different froma flame-resistant polymer-containing solution.

We succeeded in obtaining a dispersion containing a flame-resistantpolymer which can be shaped into yarns or films, by reactingpolyacrylonitrile using a nucleophile and an oxidizing agent in a polarsolvent, and have already proposed this (see WO 2005/080448 A1).

As one means to further improve productivity of a flame-resistantproduct obtained by this method, improvement in stability in a step ofproducing a shaped body, particularly, production stability in acoagulating step including a coagulation site for shaping into a yarnshape, and a washing site for removing a chemical and a solventremaining in a yarn is expected.

It could therefore be helpful to provide a dispersion containing aflame-resistant polymer which can improve shaping stability of theflame-resistant polymer during ejection from a die orifice, and physicalstability of a shaped product in a washing step.

SUMMARY

We thus provide a dispersion containing a flame-resistant polymer whichis a dispersion in which a flame-resistant polymer is dispersed in anorganic solvent, wherein a tensile strength of the flame-resistantpolymer per cross-sectional area in water is 1.0 MPa or more and 6.5 MPaor less.

According to a preferable aspect of the dispersion containing aflame-resistant polymer, the organic solvent is a polar organic solvent.

According to a preferable aspect of the dispersion containing aflame-resistant polymer, the flame-resistant polymer is obtained byheat-treating an acrylonitrile polymer. In the heat treatment, when thedispersion in which an acrylonitrile polymer is dispersed in a polarorganic solvent is heat-treated, it is preferable to add at least onekind of acid, acid anhydride or acid chloride, and it is preferable thatthe total addition amount of those acid, acid anhydride and acidchloride is in a range of 0.05 part by weight to 7.0 parts by weightbased on 10.0 parts by weight of the acrylonitrile polymer.

According to a preferable aspect of the dispersion containing aflame-resistant polymer, the acid is a carboxyl acid or a sulfonic acid,and examples of the carboxylic acid include a monocarboxylic acid suchas benzoic acid, hydroxybenzoic acid, methylbenzoic acid andaminobenzoic acid, and a dicarboxylic acid such as phthalic acid,isophthalic acid, and terephthalic acid. Examples of the sulfonic acidinclude methanesulfonic acid, toluenesulfonic acid, and an aminosulfonicacid such as taurine, sulfanilic acid, and orthanilic acid.

The dispersion containing a flame-resistant polymer can be shaped into aflame-resistant fiber, and the flame-resistant fiber can be carbonizedto produce a carbon fiber.

A dispersion containing a flame-resistant polymer in which release froman ejection port is remarkably good upon shaping of the dispersioncontaining a flame-resistant polymer is obtained. In this dispersioncontaining a flame-resistant polymer, particularly, since release at anejection die orifice site becomes good upon shaping into a yarn shape,it becomes possible to suppress single fiber breaking or adhesion at theejection die orifice site. Further, since a shaped product having a highphysical strength at coagulation is obtained, damage of the shapedproduct is considerably reduced in a step of removing a dispersingmedium remaining in the shaped product, that is, a stage of washing, astep speed can be improved. These effects are extremely remarkable uponshaping of the dispersion containing a flame-resistant polymer into ayarn shape and, particularly, the suppressing effect is great in a wetspinning method.

Further, the physical strength of a carbon fiber obtained by carbonizinga flame-resistant fiber obtained by wet-spinning the dispersioncontaining a flame-resistant polymer is also improved. Moreover, due togood release of the dispersion containing a flame-resistant polymer froma die orifice, a die orifice hole density can be increased, and spacesaving can be realized. Therefore, a production efficiency is improved.

DETAILED DESCRIPTION

In the dispersion containing a flame-resistant polymer in which aflame-resistant polymer is dispersed in an organic solvent, it isimportant that the in-water tensile strength per unit cross-sectionalarea of the flame-resistant polymer is 1.0 MPa or more and 6.5 MPa orless.

The in-water tensile strength per unit cross-sectional area is obtainedby stretching the dispersion containing a flame-resistant polymer into afilm, coagulating the film in water, cutting the coagulated film into apredetermined size, measuring the tensile strength of the film in waterwith a tensile testing machine, and by dividing its value by across-sectional area of a plane vertical to a tensile direction.

Details of a method of measuring the in-water tensile strength are asfollows. That is, about 5 g of the dispersion containing aflame-resistant polymer retained at a temperature of 40° C. is cast onone side of a glass plate sufficiently dried at a temperature of 40° C.,at a width of around 3 cm left and right from a central line, and isapplied so as to be a constant thickness with a Baker type applicator.This is immediately mildly placed into a container of 20 cm×20 cm×10 cmfilled with water conditioned at a temperature of 25° C. to 30° C., witha film plane upside. After allowing to stand for 1 minute, this is leftas it is while water conditioned at a temperature of 25° C. to 30° C.flows in a container at a rate of 200 mL per minute so as not todirectly touch the film. Subsequently, the film is cut into a size of 7mm×15 mm with one blade of a razor to obtain a film cross-section. Thefilm cross-section is slowly peeled from the glass plate, a thickness ismeasured in water at ten points, and an average value thereof is definedas a film thickness. This film cross-section having a film thickness of100 μm to 150 μm is grasped in a tensile testing equipment so that asample length site becomes 10 mm, and a tensile rate is measured inwater at a tensile rate of 20 mm/min. The measurement number n is 25,and a value obtained by dividing an average of the resulting values by across-sectional area in a direction vertical to a tensile direction isdefined as an in-water tensile strength. As the tensile testingequipment, Model 1125 manufactured by Instron is used.

This value of the in-water tensile strength per unit cross-sectionalarea is defined as an index of the coagulation hardness of thedispersion containing a flame-resistant polymer. When a flame-resistantpolymer having a value of 1.0 MPa or more and 6.5 MPa or less is shaped,step stability of the shaped product is improved, particularly, singlefiber breaking at a coagulating step in a coagulation bath upon shapinginto a yarn shape, and a washing step of removing a dispersing medium issuppressed, and a flame-resistant fiber having an excellent quality isobtained. Further, when this flame-resistant fiber is carbonized by anormal method, as compared with a carbon fiber derived from a dispersioncontaining another flame-resistant polymer, a carbon fiber excellent ina physical strength can be obtained.

When the in-water tensile strength per unit cross-sectional area is 2.0MPa or more and 6.5 MPa or less in the aforementioned range, fusionbetween fibers in a drying step is suppressed. Further, when thein-water tensile strength per unit cross-sectional area is 3.0 MPa ormore and 6.5 MPa or less, by increasing a stretching rate at a spinningstep and a drying step, it becomes remarkably easy to improve anorientation property of a fiber.

The flame-resistant polymer is a polymer having flame resistance, andthe dispersion containing a flame-resistant polymer is a dispersion inwhich a flame-resistant polymer as a component is dispersed in anorganic solvent. Herein, the dispersion is a viscous fluid, and adispersion having fluidity upon shaping and molding may be used, notonly having fluidity at a normal temperature, but also a solid and a gelhaving no fluidity at a certain temperature are included, including allhaving fluidity at around a processing temperature by heating and ashearing force.

As a back pressure at a die orifice during processing of the dispersioncontaining a flame-resistant polymer is lower, the dispersion can bemore easily ejected, while when a certain viscosity is too low, anobjective shaped form is obtained with difficulty in some cases. Forthis reason, a solution viscosity of the dispersion containing aflame-resistant polymer measured with a B-type viscometer at aprocessing temperature is preferably 1 Pa·s or more and 10 0 Pa·s orless, more preferably 2.5 Pa·s or more and 50 Pa·s or less.

In the dispersion containing a flame-resistant polymer, it is preferablethat a content of the flame-resistant polymer is 5 parts by weight ormore and 45 parts by weight or less based on the total amount of thedispersion containing a flame-resistant polymer. When the content of theflame-resistant polymer is lower than 5 parts by weight, the quality isdeteriorated such as opening of a hole in a molded product at shaping ofthe dispersion containing a flame-resistant polymer in some cases, whilewhen the content is higher than 45 parts by weight, fluidity of thedispersion containing a flame-resistant polymer is reduced, and shapingbecomes difficult in some cases. The content of the flame-resistantpolymer is more preferably 6 parts by weight or more and 30 parts byweight or less.

As an organic solvent, a polar organic solvent is preferably used. Thepolar organic solvent preferably has a relative permittivity as measuredwith an LCR meter under a normal temperature of preferably 2 or more,more preferably 10 or more. When the relative permittivity is such avalue, it is possible to more stably disperse the flame-resistantpolymer, dispersing medium extraction at coagulation process is easy,and handling is easy. When the relative permittivity is too small,extraction of a dispersing medium becomes difficult at use of an aqueouscoagulation bath at a coagulation process. In addition, the relativepermittivity has not particularly an upper limit, but when the upperlimit is too great, it becomes difficult to stably disperse theflame-resistant polymer in some cases. Therefore, it is preferable touse a polar organic solvent having a relative permittivity of 80 orless.

Examples of the polar organic solvent preferably include dimethylsulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF),dimethylacetamido (DMAc), sulfolane, dimethylimidazolidione, ethyleneglycol and diethylene glycol. As the polar organic solvent, DMSO, NMP,DMF and DMAc are more preferable and, among them, from a view point of amagnitude of solubility in a salt, DMSO and DMF are particularlypreferably used. These polar organic solvents may be used alone, or twoor more kinds may be used by mixing.

It is preferable that the content of the organic solvent is 45 parts byweight or more and 95 parts by weight or less based on the total amountof the dispersion containing a flame-resistant polymer. When the contentof the organic solvent is less than 45 parts by weight, dispersingstability of the dispersion containing a flame-resistant polymer isremarkably reduced, and fluidity is lost in some cases, while when thecontent of the organic solvent is more than 95 parts by weight, aviscosity of the dispersion containing a flame-resistant polymer isreduced, and shaping itself becomes difficult in some cases.

Flame resistance has substantially the same meaning as that of a term“flameproof,” and is used including the meaning of a term of “flameretardant.” Specifically, flame resistance is a generic name indicatinga nature that firing continues with difficulty, that is, a material isburnt with difficulty. As the mean for specifically assessingflame-resistance performance, for example, a method of testing flameproofness of a thin material (45° Merker Burner method) is described inJIS Z 2150 (1966). A sample to be assessed (board, plate, sheet, film,thick fabric and the like having a thickness of less than 5 mm) isheated with a burner for a specific time, and determination can beperformed by assessing a flame remaining time and a carbonization lengthafter firing. As a flame remaining time is shorter, or as acarbonization length is shorter, it is determined that flame resistance(flameproof) performance is excellent. In the case of a fiber product, amethod of testing burning of a fiber is described in JIS L 1091 (1977).After a test by this method, flame resistance performance can bedetermined similarly by measuring a carbonization area and a flameremaining time.

There are various shapes/forms of a flame-resistant polymer and aflame-resistant molded article, and a degree of flame resistanceperformance is over a wide range from very high flame resistance of nofiring to a some extent of continuous burning after firing. A subject isone which is recognized at not less than a level determined for flameresistance performance by a specific assessing method shown in Examplesdescribed later. Specifically, excellent or better in flame resistanceperformance in a method of assessing flame resistance described later ispreferable. Particularly, at a stage of a flame-resistant polymer, ashape/form of a polymer varies depending on isolation condition, and aconsiderable scatter is easily included as a nature of flame resistanceand, therefore, a method of assessment after molding into a constantshape is adopted.

A flame-resistant molded article such as a flame-resistant fiberobtained by molding a flame-resistant polymer can be also measuredsimilarly by the specific means of assessing flame resistance shown inExamples described later.

A flame-resistant polymer, a precursor of which is an acrylonitrilepolymer, has a structure which is chemically similar to that of aflame-resistant polymer obtained by heating a fibrous acrylonitrilepolymer in the air. Although a structure of both flame-resistantpolymers has not been completely clarified, it is thought that thosepolymers have naphthyridine ring, acrydone ring and hydrogenatednaphthyridine ring structures generated by a cyclization reaction or anoxidization reaction of a nitrile group, as described in referenceswhich analyze an acrylonitrile flame-resistant fiber (Journal of PolymerScience Part A: Polymer Chemistry) (J. Polym. Sci. Part A: Polym.Chem.), 1986, vol. 24, p. 3101. A flame-resistant polymer dispersed inan organic solvent has no disorder even when an unreacted nitrile groupremains, as far as flame resistance is not deteriorated, and has nodisorder even when a minor amount of a crosslinking bond is generatedbetween molecules, solubility is not deteriorated. From such aviewpoint, the acrylonitrile polymer which is a precursor of theflame-resistant polymer may be straight, or branched. Alternatively, thepolymer may contain, in a skeleton thereof, other copolymerizationcomponent such as acrylate or methacrylate and vinyl compounds randomlyor as a block.

The molecular weight of the flame-resistant polymer may be a molecularweight having a viscosity depending on a molding method, and it ispreferable that the mass average molecular weight (Mw) of a precursorpolymer as measured by gel permeation chromatography (GPC) is 1000 to1000000. When the mass average molecular weight of the precursor polymeris lower than 1000000, a necessary time for flame-resisting can beshortened, but since intermolecular interaction such as a hydrogen bondbetween heat-resistant polymers becomes weak, it becomes possible toattain a sufficient strength in a shaped molded article. On the otherhand, when the mass molecular weight of the precursor polymer exceeds1000000, since a time necessary for thermostabilization becomes longer,the production cost is increased, and molecular interaction due to ahydrophobic bond between flame-resistant polymers becomes too strong,the polymer is gelled at cooling, and it becomes difficult to obtainfluidity of the dispersion containing a flame-resistant polymer at ashaping temperature, in some cases. The mass average molecular weight ofthe precursor polymer is more preferably 10000 to 50000, furtherpreferably 20000 to 300000.

The chemical structure of the flame-resistant polymer is preferably suchthat a solution thereof is measured with a nuclear magnetic resonanceapparatus (NMR) for 13-C, and the structure has a signal in a range of150 to 200 ppm, and is preferable that the structure has a maximumabsorption peak at around 1600 cm⁻¹ by infrared spectrometry (IR). Whenthe polymer has a peak in a range by both measuring methods, it can besaid to be a flame-resistant polymer having particularly highheat-resistance.

A flame-resistant polymer may be obtained by heat-treating either of asolid single material of an acrylonitrile polymer as a precursor, or apolymer in the state where it is dispersed in an organic solvent. Sincea solid of the flame-resistant polymer has low affinity for a polarsolvent, and is dispersed with difficulty in some cases, the latterprocedure is preferable.

When a dispersion of an acrylonitrile polymer as a precursor isheat-treated to perform flame-resisting, condition of a temperature, atime and an apparatus, and a procedure are not particularly limited asfar as flame-resisting progresses. A heating method is not particularlylimited, any industrially sold heating apparatus, a representative ofwhich is a jacket heating medium circulation, a mantle heater, an oilbath or an immersion heater may be used. However, when flame-resistingis performed at a high temperature, since a risk of bumping of asolvent, and ignition or inflammation is increased, it is preferable toperform flame-resisting at a boiling point of a solvent used or lower.In addition, regarding a reaction time, since a flame-resisting reactionis an exothermic reaction, a reaction in a short time makes heat removaldifficult, leading to a runaway reaction in some cases and, therefore,it is preferable to adjust the reaction time to 30 minutes or longer. Onthe other hand, when flame-resisting is performed over a long period oftime, a production amount per unit time is reduced, and therefore thisis non-productive, a reaction time is preferably within 24 hours, morepreferably 1 hour or longer and 12 hours or shorter.

When flame-resisting is performed by heat-treating a dispersion of anacrylonitrile polymer as a precursor, a reaction can progress at a lowtemperature of 160° C. or lower by using an oxidizing agent and acyclizing agent, being a preferable aspect.

The oxidizing agent is a compound having an action of extracting ahydrogen atom from a precursor polymer by a reaction, or an action ofdonating an oxygen atom, and specific examples of the oxidizing agentinclude a nitro-based compound and a quinone-based compound from a viewpoint of safety and reactivity.

As the nitro-based compound, from heat stability at a reaction, amononitro compound having an aromatic ring is more preferable, examplesinclude nitrobenzene, o-, m-, and p-nitrotoluene, o-, m-, andp-nitrophenol, nitroxylene and nitronaphthalene, and nitrobenzene ando-, m-, and p-nitrotoluene are particularly preferably used. Examples ofthe quinone-based compound include 1,4-benzoquinone, chloranil,bromanil, chloro-1,4-benzoquinone, dichloro-1,4-benzoquinone,bromo-1,4-benzoquinone, dibromo-1,4-benzoquinone,tetrafluoro-1,4-benzoquinone, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone,orthobenzoquinone, orthochloranil and orthobromanil, and1,4-benzoquinone, chloranil, dichloro-1,4-benzoquinone, and2,3-dichloro-5,6-dicyano-1,4-benzoquinone are particularly preferablyused.

The addition amount of these oxidizing agents is not particularlylimited, but is preferably 0.01 to 20.0 parts by weight, more preferably0.1 to 10.0 parts by weight based on 10.0 parts by weight of theprecursor polymer. These oxidizing agents may be used alone, or may beused by mixing two or more kinds.

The cyclizing agent is a compound which derives a non-cyclic skeletalsite into a cyclic structure by generation of a bond, and specificexamples of the cyclizing agent include organic nucleophiles such asamine-based compounds, guanidine-based compounds, alcohol-basedcompounds, aminoalcohol-based compounds, carboxylic acid-basedcompounds, thiol-based compounds, and amidine-based compounds, metalalkoxide compounds, metal amide compounds, metal imide compounds, metalhydrides, metal hydroxides and metal carbonates and carboxylic acidmetal salts. From a viewpoint of a magnitude of a cyclization efficiencyand stability of a reagent, amine-based compounds, guanidine compounds,amino alcohol compounds, metal alkoxide compounds and metal imidecompounds are preferably used. Among them, from a viewpoint ofdispersing property of the flame-resistant polymer, amino alcohol-basedcompounds are particularly preferably used.

As the amine-based compounds, any compound may be used as far as it hasan amine skeleton, and examples include ammonia, methylamine,ethylamine, propylamine, butylamine, allylamine, pentylamine,octylamine, dodecylamine, aniline, benzylamine, toluidine,ethylene-diamine, propanediamine, cyclohexanediamine, decamethylenediamine, 3,5-pyridinediamine, N,N-dimethylethylenediamine,N,N-diethylethylenediamine, 3,5-dimethylbenzene-2,4-diamine, and1,12-dodecanediamine.

As the guanidine-based compounds, any compound may be used as far as ithas a guanidine structure, and examples include guanidine carbonate,guanidine thiocyanate, guanidine acetate, guanidine phosphate, guanidinehydrochloride, guanidine nitrate, guanidine sulfate, methylguanidine,ethylguanidine, dimethylguanidine, aminoguanidine, phenylguanidine,naphthylguanidine, nitroguanidine, nitrosoguanidine, acetylguanidine,cyanoguanidine, and guanyl-urea, and guanidine carbonate, guanidineacetate and guanidine phosphate are particularly preferably used.

Examples of the amino alcohol-based compounds include monoethanolamineand diethanolamine, examples of the propanolamine metal alkoxidecompounds include potassium tert-butoxide, sodium tert-butoxide,potassium methoxide, sodium methoxide, potassium ethoxide, sodiumethoxide, potassium isopropoxide, sodium isopropoxide, potassiumisobutoxide, sodium isobutoxide, and sodium phenoxide, and potassiumtert-butoxide and sodium tert-butoxide are particularly preferably used.

Examples of the metal imide compounds include potassium phthalimide andsodium phthalimide and, among them, potassium phthalimide is preferablyused.

The addition amount of these cyclizing agents is not particularlylimited, but is preferably 0.01 to 50.0 parts by weight, more preferably0.1 to 20.0 parts by weight, further preferably 0.3 to 10.0 parts byweight based on 10.0 parts by weight of the precursor polymer.

To obtain the flame-resistant polymer having an in-water tensilestrength per unit cross-sectional area of 1.0 MPa or more and 6.5 MPa orless, it is preferable to add an acid when a dispersion of anacrylonitrile polymer is heat-treated. The acid may be added before heattreatment, or during heat treatment.

The acid as used herein may be defined as either of an acid defined asan acid by donating and accepting a proton, or an acid defined as anacid by donating and accepting an electron. Alternatively, two or morekinds among them may be used by mixing.

Specifically, examples of the acid defined as an acid by donating andaccepting a proton include preferably inorganic acids such ashydrochloric acid, nitric acid, sulfuric acid, phosphoric acid andhydrobromic acid, carboxylic acids such as formic acid, acetic acid,propionic acid, butyric acid, isobutyric acid, valeric acid, caproicacid, enanthic acid, carpylic acid, pelargonic acid, capric acid, lauricacid, myristic acid, palmitic acid, margaric acid, stearic acid, oleicacid, linoleic acid, linolenic acid, arachidonic acid, benzoic acid,methylbenzoic acid, phthalic acid, fumaric anhydride, isophthalic acid,terephthalic acid, salicylic acid, gallic acid, pyruvic acid, lacticacid, malic acid, citric acid, oxalic acid, malonic acid, succinic acid,fumaric acid, maleic acid, aconitic acid, glutaric acid, adipic acid,feruloyl, hydroxybenzoic acid, homo-salicylic acid, pyrochatechuic acid,resorcylic acid, gentisic acid, vanillic acid, isovanillic acid,orsenillic acid, asaronic acid, mandelic acid, phthalonic acid, benzilicacid, phloretic acid, tropic acid and coumaric acid, and sulfonic acidssuch as methanesulfonic acid, trifluoromethane-sulfonic acid,ethanesulfonic acid, taurine, propanesulfonic acid,hydroxypropanesulfonic acid, benzenesulfonic acid, tosylic acid,camphorsulfonic acid, orthanilic acid, metanilic acid, sulfanilic acid,naphthalenesulfonic acid, and aminonaphthalenesulfonic acid.

A carboxylic acid and a sulfonic acid referred herein are a generic nameof a compound having a carboxyl group or a sulfonic acid group,respectively, and may have other functional group such as a hydroxygroup and an amino group in a molecule.

In addition, examples of the acid defined by donating and accepting anelectron include Lewis acids such as aluminum chloride, zinc chloride,iron chloride, silver triflate, iron cyanide and copper chloride.

Among them, from a viewpoint of availability in a large amount and at alow cost, and inclusion of no metal, it is preferable to use acarboxylic acid or a sulfonic acid which has little environmental load,and excellent in a handling property at a large scale. Among carboxylicacids, a carboxylic acid which has high solubility in a polar solventused in a reaction, has a high boiling point and can set a reactiontemperature to be high, specifically, a monocarboxylic acid such asbenzoic acid, hydroxybenzoic acid, methylbenzoic acid, and aminobenzoicacid, and a dicarboxylic acid such as phthalic acid, isophthalic acidand terephthalic acid are preferably used.

Among them, phthalic acid and isophthalic acid and terephthalic acidwhich are a dicarboxylic acid are preferable, and yarn breaking at aspinning step is further dramatically reduced, and step stability isimproved. This is considered as follows: due to the presence of twocarboxyl groups in one molecule of an acid, crosslinking occurs betweenflame-resistant polymers, and interaction due to entanglement betweenthe flame-resistant polymers is increased.

Regarding a sulfonic acid, since a boiling point of methanesulfonic acidhaving a small molecular weight is 167° C., a reaction temperature canbe set high even when any compound is selected, therefore, any ispreferably used as far as it is a compound having a sulfonic acid group.However, since aminosulfonic acid which is a sulfonic acid having anamino group in a molecule can improve coagulation hardness of theflame-resistant polymer without inhibiting nucleophilic ability of acyclizing agent, it is further preferable. That is, when aminosulfonicacid is used, there is also the effect of reducing an addition amount ofa cyclizing agent, and it is possible to save a raw material and awaste. Among them, because of industrially easy availability, taurineand sulfanilic acid can be particularly preferably exemplified.

Like the acid, an acid anhydride and an acid chloride can be alsopreferably used. An acid anhydride mentioned herein refers to a compoundin a form that two acyl groups share an oxygen atom, by losing onemolecule of water from two carboxyl groups of a carboxylic acid definedin the Dictionary of Chemistry (Tokyo Kagaku Dojin). Specific examplesof the acid anhydride preferably include adipic anhydride, succinicanhydride, butyric anhydride, citric anhydride, tartaric anhydride,hexanoic anhydride, benzoic anhydride and phthalic anhydride.

In addition, the acid chloride refers to a compound in which a hydroxylgroup contained in a carboxyl group of carboxylic acid defined in theDictionary of Chemistry (Tokyo Kagaku Dojin) is substituted withchlorine. Specific examples of the acid chloride preferably includeacetyl chloride, propionyl chloride, pivaloyl chloride, butanoylchloride, benzoyl chloride, anisole chloride, naphthoyl chloride andphthaloyl dichloride.

When an amount of an acid, an acid anhydride and an acid chloride to beadded to the dispersion containing a precursor polymer which is anacrylonitrile polymer is small, the clear effect is seen little. On theother hand, when a large amount of an acid or the like is added,progression of a flame-resisting reaction becomes slow, and a precursorpolymer is precipitated in some cases. Therefore, the total additionamount of the acid, the acid anhydride and the acid chloride is in arange of preferably 0.05 part by weight to 7.0 parts by weight, morepreferably 0.1 part by weight to 5.0 parts by weight based on 10.0 partsby weight of the precursor polymer.

Specifically, for example, the addition amount of an acid when anacrylonitrile polymer is used as a precursor polymer, and a dicarboxylicacid is used as an acid is preferably in a range of 0.05 part by weightto 5.0 parts by weight based on 10.0 parts by weight of theacrylonitrile polymer. When the addition amount of the acid is more than50 parts by weight, dispersing stability of the dispersion containing aflame-resistant polymer is reduced, and fluidity is easily lost in somecases. The addition amount of the acid is further preferably in a rangeof 0.1 part by weight to 2.0 parts by weight.

A method of removing a dispersing medium from a dispersion containing ashaped flame-resistant polymer is not particularly limited, but examplesinclude a method of evaporating a dispersing medium from a dispersioncontaining a shaped flame-resistant polymer by heating or reduction in apressure, a method of immersing a dispersion containing a shapedflame-resistant polymer in a coagulation solution, and extracting adispersing medium into the coagulation solution, and the like. A methodof extracting a dispersing medium into a coagulation solution which issimple in control, and has high productivity of a process is preferable.

As the coagulation solution, a poor solvent of the flame-resistantpolymer, which is compatible of the dispersing medium is preferablyused. It is preferable to use an aqueous coagulation solution as thecoagulation solution and, to make recovery of an extracted dispersingmedium easy, it is preferable to use a coagulation solution of a mixturesystem of water, and a solvent which is the same kind as that of adispersing medium used in the dispersion containing a flame-resistantpolymer. A solvent other than the dispersing medium used in thedispersion containing a flame-resistant polymer may be mixed into thesecoagulation solutions and, from a viewpoint of solvent recovery, it ispreferable to constitute a coagulation solution only of water, and asolvent which is the same kind as that of the dispersing medium used inthe dispersion containing a flame-resistant polymer. Further, a mixingratio of water and a solvent in the coagulation solution is preferably1:9 to 9:1, more preferably 2:8 to 8:2, further preferably 3:7 to 7:3.Adopting of such a mixing ratio is also allowed to control a coagulationrate, and properties depending on utility can be also controlled by thecoagulation solution. In addition, the coagulation solution may containan inorganic salt, a pH adjusting agent, a step treating agent, and areaction promoting agent of a dispersion as a compound which makesextraction of a dispersing medium easy.

As a method of shaping the dispersion containing a flame-resistantpolymer into a fiber, methods such as a wet spinning method, a dry wetspinning method, a dry spinning method, a flash spinning method, anelectrospinning method, a spunbond method, a melt blow method and acentrifugal force spinning method can be adopted. Among them, a wetspinning method and a dry wet spinning method have high productivity,and are preferably applied. Particularly, in the wet spinning method,since a dispersing medium begins to be removed immediately after shapingof the dispersion containing a flame-resistant polymer, productivity ishigh, and even when a fiber strength immediately after shaping is low, afiber can be run at a low rate, and handling is easy. The wet spinningmethod mentioned herein is a method of introducing the dispersioncontaining a flame-resistant polymer into a die orifice having aplurality of holes after weighing/filtration, ejecting the dispersionthrough a die orifice hole by a pressure applied to the dispersioncontaining a flame-resistant polymer to shape it, and immediatelycoagulating the shaped dispersion with a coagulation solution. Inaddition, the dry wet spinning is a method of ejecting the dispersioncontaining a flame-resistant polymer through the die orifice hole toshape it, running the ejected dispersion in an air phase, andcoagulating it with a coagulation solution.

As a material of the die orifice used herein, SUS, gold and platinum canbe conveniently used. In addition, it is a preferable aspect from aviewpoint of reduction in a scatter of a single fiber cross-sectionalarea in an aggregate of the resulting flame-resistant fiber that beforethe dispersion containing a flame-resistant polymer is flown into thedie orifice hole, the dispersion containing a flame-resistant polymer isfiltered or dispersed using a sintered filter of an inorganic fiber, ora woven fabric, a knitted fabric and a non-woven fabric consisting of asynthetic fiber such as a polyester fiber and a polyamide fiber as afilter.

A die orifice hole diameter in a range of preferably 0.01 to 0.5 mm, anda hole length in an arbitrary range of preferably 0.01 to 1 mm can beused. In addition, any of a die orifice hole number in a range ofpreferably 10 to 1000000 can be used. As hole arrangement, any alignmentsuch as zigzag alignment can be used, and the dispersion may bepre-divided so as to easily perform fiber separation.

It is preferable that a coagulation step, when wet spinning isperformed, uses a combination of two or more coagulation baths. A firstbath forms a flame-resistant polymer into a yarn shape, a second orafter bath removes reagents and a dispersing medium remaining in acoagulated yarn, that is, washing, thereby, a coagulation bath as awhole can be compact.

A temperature of the coagulation solution can be an arbitrarytemperature of a coagulation point or higher and a boiling point orlower of a coagulation solution in the first bath, and can beconveniently adjusted in conformity with a coagulation property and steppassability of the flame-resistant polymer.

To make a structure of a coagulated yarn compact, it is preferable thata temperature of the coagulation solution is in a range of 20° C. orhigher and 40° C. or lower. In addition, in the second or after bathhaving a main object of washing, an arbitrary temperature of acoagulation point or higher and a boiling point or lower of thecoagulation solution is possible, and when water is used in thecoagulation solution, it is preferable that a temperature of thecoagulation solution is 60° C. or higher and 85° C. or lower. Byadopting such a temperature of the coagulation solution, reagents and adispersing medium remaining in the yarn formed in the first bath areeffectively extracted. In addition, it is preferable that theconcentration of a poor solvent in the coagulation solution is increasedwith passage through a coagulation step.

It is preferable that a lubricant described later is imparted to a fiberyarn in the water-swollen state after water washing and stretching. As amethod of imparting a lubricant, in view of that the lubricant can beuniformly imparted into the interior of a fiber yarn, a method may bearbitrarily selected and used and, specifically, means such as immersionof a fiber yarn into a lubricant bath, and spraying and additiondropwise to a running fiber yarn are adopted. It is preferable that theconcentration of the lubricant upon impartation herein is in a range of0.01 to 20% by weight. Herein, the lubricant consists of, for example, amain lubricant component such as silicone and a diluent component fordiluting it, and a lubricant concentration is a ratio of a content of amain lubricant component relative to a total lubricant.

The adhesion amount of a lubricant component is such that a ratio of anet matter relative to a dry weight of a fiber yarn is in a range ofpreferably 0.1 to 5% by weight, more preferably 0.3 to 3% by weight,further preferably 0.5 to 2% by weight. When the adhesion amount of thelubricant component is too small, fusion between single yarns occursand, when the adhesion amount is too great, a burning scatter at firingreduces a tensile strength of the resulting carbon fiber, in some cases.

As a method of drying a fiber yarn, a method of directly contacting afiber yarn with a plurality of dried and heated rollers, a method ofsupplying hot air or water steam to a fiber yarn, a method ofirradiating a fiber yarn with infrared-ray or electromagnetic wave at ahigh frequency, and a method of bringing out the pressure-reduced statecan be conveniently selected and combined. Normally, when the hot air issupplied, this can be performed by supplying the hot air in parallelwith, or orthogonal with a running direction of a fiber yarn. Asradiation heating-system infrared-ray, far infrared-ray,mid-infrared-ray and near infrared-ray can be used, and irradiation witha microwave can be also selected. A drying temperature can bearbitrarily in a range of around 50 to 450° C. and, generally, in thecase of a low temperature, a long time is required and, in the case of ahigh temperature, the yarn can be dried in a short time.

A molded material of a fiber or the like obtained by shaping and moldingthe dispersion containing a flame-resistant polymer contains many voidsin some cases. In many cases, it is desirable that a mechanical strengthof the molded material is further increased. As the means to improvethis mechanical strength, it is preferable that the means is via asintering/firing step of closing voids by heat-treating the moldedarticle obtained as described above.

In the step, the condition such as a temperature profile and a steppassage rate depends on a material, and the molded article isheat-treated preferably at a temperature which is lower than a softeningtemperature of the molded article by 50° C., more preferably at asoftening point or higher. At a treating temperature lower than(softening point temperature −50° C.), it is difficult to close voidscontained in the molded article. In addition, there is particularly noupper limit of a temperature, but when the molded article is softened,and a shape is retained with difficulty, it is preferable to rise atreating temperature at a few stages, or continuously rise a treatingtemperature.

In addition, when a softening point thereof is lowered with aplasticizer, sintering/firing can be performed while a thermaldegradation reaction is suppressed. A component of the plasticizer maybe contained in the dispersion containing a flame-resistant polymer inadvance, and from a viewpoint of recovery of a dispersing mediumcontaining a flame-resistant polymer, it is preferable that thecomponent is imparted between a coagulation step and a sintering/firingstep. The plasticizer is not particularly limited as far as it lowers asoftening point, and from a viewpoint of uniform impartation to themolded article, and dispersing into a dispersion, it is preferable thatthe plasticizer is a liquid. Inter alia, it is a preferable aspect touse water which is friendly to the environment and has high safety, andit is a further preferable aspect to use water containing a surfactant,to improve an adhering property to a yarn.

In heat treatment when the molded article of a fiber or the like isconverted into a sintered/fired body, a chemical structure of the moldedarticle may be changed. For example, in the case where theflame-resistant polymer is a condensed-based polymer compound, amolecular weight thereof is increased by solid phase polymerizationunder the vacuum atmosphere and, in the case where the polymer is aflame-resistant polymer having an acridone skeleton or a pyrimidineskeleton, it changes into a graphite structure in some cases. Thesechanges are made to occur after voids contained in the molded articleare once decreased by heat treatment. By doing this, a sintered/firedbody having little voids, and excellent in mechanical properties can beobtained.

Heat treatment when the molded article is converted into asintered/fired article may be not accompanied with change in a chemicalstructure of the molded article. For example, in the case of silica andtitania obtained by a sol-gel transition method, by heat treatment at asuitable temperature, not only voids between particles are substantiallyclosed, but also a suitable sintered/fired article is obtained.

In addition, in a heat treating step upon firing/sintering, deformationsuch as stretching and compression may be imparted to the moldedarticle. By these deformations, a form of the resulting fired/sinteredarticle becomes more preferable, and mechanical properties thereof andother properties can be improved.

A shaped and molded flame-resistant fiber may exhibit a form of a fiberaggregate such as a multifilament and the like. A carbon fiber aggregatecan be obtained by heat-treating, under the inert atmosphere, so-calledcarbonization-treating a flame-resistant fiber aggregate. The carbonfiber aggregate can be obtained by heat-treating the flame-resistantfiber aggregate at a highest temperature in a range of suitably 300° C.or higher and lower than 2000° C. in the inert atmosphere. Morepreferably, as a lower part of a highest temperature, 800° C. or higher,1000° C. or higher, and 200° C. or higher are preferable in this orderand, as a higher part of a highest temperature, 1800° C. or lower can bealso used. Alternatively, the resulting carbon fiber aggregate isfurther heat-treated at a temperature of preferably 2000 to 3000° C. inthe inert atmosphere, thereby, a carbon fiber aggregate having adeveloped graphite structure can be also obtained.

As a strength of the resulting carbon fiber aggregate, 100 MPa or more,200 MPa or more, and 300 MPa or more are preferable in this order, andas a greater part of a strength, 10000 MPa or less, 8000 MPa or less,and 6000 MPa or less are suitable in this order. When the strength istoo low, the aggregate cannot be used as a reinforcing fiber in somecases. A higher strength is more preferable, but when the strength is1000 MPa, this is sufficient in many cases.

In addition, the fiber diameter of a single fiber constituting a carbonfiber aggregate is preferably 1 nm to 7×10⁴ nm, more preferably 10 to5×10⁴ nm, further preferably 50 to 10⁴ nm. When the fiber diameter isless than 1 nm, a fiber is easily broken in some cases and, when thefiber diameter is more than 7×10⁴ nm, there is a tendency that a defectis easily generated conversely.

In addition, the specific gravity of the carbon fiber aggregate obtainedis preferably 1.3 to 2.4, more preferably 1.6 to 2.1, further preferably1.6 to 1.75. When the specific gravity less than 1.3, a fiber is easilybroken in some cases and, when the specific gravity is more than 2.4,there is a tendency that a defect is easily generated conversely. Thespecific gravity can be measured by a liquid immersion method or afloating and sinking method. Herein, the carbon fiber single fiber maycontain a hollow part like a hollow fiber. In this case, the hollow partmay be continuous, or discontinuous.

The resulting carbon fiber aggregate can be electrolysis-treated tomodify a surface thereof. As an electrolysis solution used inelectrolysis treatment, acidic solutions such as sulfuric acid, nitricacid and hydrochloric acid, or alkalis such as sodium hydroxide,potassium hydroxide, and tetraethylammonium hydroxide, or salts thereofcan be used as an aqueous solution. Herein, the amount of electricityrequired in electrolysis treatment can be conveniently selecteddepending on a carbon fiber to be applied.

By electrolysis treatment, adherability between a carbon fiber materialand a matrix in the obtained composite material can be made to besuitable, and a problem of brittle destruction of a composite materialdue to too strong adhesion, and reduction in a tensile strength in afiber length direction, and a problem that a tensile strength in a fiberlength direction is high, but adherability with a resin is inferior, anda strength property in a transverse direction of a fiber is notmanifested are solved, and the balanced strength property becomes to bemanifested in the resulting composite material.

Thereafter, to impart convergence to the resulting carbon fiberaggregate, a sizing agent can be also imparted. As the sizing agent, asizing agent having good compatibility with a resin can be arbitrarilyselected depending on a kind of resin to be used.

Specifically, when the carbon fiber aggregate is obtained from theflame-resistant polymer via a flame-resistant fiber aggregate, spinningof a flame-resistant polymer containing solution to obtain aflame-resistant fiber aggregate, and up to carbonization treatment arecontinuously performed without a winding step, surface treatment andsizing agent imparting step are further included, thus, the carbon fiberaggregate can be produced by one continuous process.

From a viewpoint of the lower cost, a process for continuously producingthe carbon fiber aggregate by one process from the flame-resistantpolymer to the carbon fiber aggregate can be adopted.

EXAMPLES

Our dispersions, fibers and methods will be specifically explained byway of Examples. Each physical property value and properties in eachExample were measured by the following methods.

Tensile Strength Per Unit Cross-Sectional Area in Water

About 5 g of a flame-resistant polymer dispersion retained at atemperature of 40° C. was cast on one side of a glass plate which hadbeen sufficiently dried at a temperature of 40° C., at a width of around3 cm left and right from a central line, and was applied with a Bakertype applicator so that a thickness became constant. This wasimmediately mildly placed into a container of 20 cm×20 cm×10 cm filledwith water conditioned at a temperature of 25° C. to 30° C., with a filmplane upside. After allowing to stand for 1 minute, this was left as itis while water conditioned at a temperature of 25° C. to 30° C. flowedin a container at a rate of 200 mL per minute so as not to directlytouch the film. Subsequently, the film was cut into a size of 7 mm×15 mmwith one blade of a razor to obtain a film cross-section. The filmcross-section was slowly peeled from a glass plate, a thickness wasmeasured in water at ten points, and an average thereof was defined as afilm thickness. This film cross-section having a film thickness of 100μm to 150 μm was grasped in a tensile testing equipment so that a samplelength site became 10 mm, and a tensile rate was measured in water at atensile rate of 20 mm/min. The measurement number n was 25, and a valueobtained by dividing an average of the resulting values with across-sectional area in a direction vertical to a tensile direction wasdefined as an in-water tensile strength. As the tensile testingequipment, Model 1125 manufactured by Instron was used.

Assessment of Yarn Breaking at Washing-I

A flame-resistant polymer dispersion conditioned at a temperature of 30°C. was passed through a sintered filter, and a fiber yarn was wound at arate of 1.3 m/min while the dispersion was ejected at a rate of 10 ccper minute in a coagulation bath consisting of 55 parts by weight ofdimethyl sulfoxide and 45 parts by weight of water conditioned at atemperature of 30° C. through a die orifice having 1000 holes of a holediameter of 0.05 mm, the yarn was immediately wound in a water bathconditioned at a temperature of 70° C. at a rate of 1.7 m/min for 3hours without drying, single fibers floating or settling in the waterbath were filtered and collected and, when the mass after dried at 120°C. for 2 hours was 0 mg or more and less than 15 mg, this was defined asexcellent (⊚) and, when the mass was 15 mg or more and less than 50 mg,this was defined as good (◯) and, when the mass was 50 mg or more, thiswas defined as worse (x), thus, assessment was performed.

Assessment of Yarn Breaking at Washing-II

A flame-resistant polymer dispersion conditioned at a temperature of 30°C. was passed through a sintered filter, and a fiber yarn was wound at arate of 3.0 m/min while the dispersion was ejected at a rate of 10 ccper minute into a coagulation bath consisting of 55 parts by weight ofdimethyl sulfoxide and 45 parts by weight of water conditioned at atemperature of 30° C. through a die orifice having 1000 holes of a holediameter of 0.05 mm, the yarn was immediately wound in a water bathconditioned at a temperature of 70° C. at a rate of 6.0 m/min for 3hours without drying, single fibers floating or settling in the waterbath were filtered and collected and, when the mass after dried at 120°C. for 2 hours was 0 mg or more and less than 15 mg, this was defined asexcellent (⊚) and, when the mass was 15 mg or more and less than 50 mg,this was defined as good (◯) and, when the mass was 50 mg or more, thiswas defined as worse (x), thus, assessment was performed.

Isolation of Flame-Resistant Polymer and Measurement of Concentration

A dispersion containing a flame-resistant polymer was weighed, about 4 gwas placed into 500 ml of water, and this was boiled. A solid was takenout once, placed in 500 ml of water again, and this was boiled. Aremaining solid matter was placed on an aluminum pan, and dried in anoven at a temperature of 120° C. for 1 hour, and a flame-resistantpolymer was isolated. An isolated solid matter was weighed, a ratiorelative to a weight of the original dispersion containing aflame-resistant polymer was calculated to obtain a concentration.

NMR Measurement of Flame-Resistant Polymer

An NMR spectrum of a flame-resistant polymer was measured at roomtemperature at a measurement nuclear frequency of 67.9 MHz, and aspectrum width of 15015 kHz using a spectrum of the known solvent as aninternal standard. As an apparatus, GX-270 manufactured by JEOL Ltd. wasused.

IR (Infrared Spectrophotometer) Measurement

After a heat-resistant polymer was subjected to removal of a solvent inhot water at a high temperature, IR was measured using FT-IR measuringinstrument (manufactured by Shimadzu) using a tablet obtained bygrinding and mixing 2 mg of a lyophilized material and 300 mg of KBr forinfrared absorption with a mortal, and processing the mixture withtablet molding equipment.

Measurement of Specific Gravity of Fiber

An automatic specific gravity measuring apparatus by a liquid immersionmethod, equipped with an electron balance was made by ourselves, andmeasurement was performed according to JIS Z 8807 (1976). As a liquid,ethanol was used, and a sample was placed therein, followed bymeasurement. A sample was sufficiently wetted in another bath usingethanol before placement in advance, and a defoaming procedure wasperformed.

Method of Assessing Flame-Resistance of Fiber

A bundle-like fiber aggregate consisting of 1500 single fibers washeated with a flame of a Merker Burner having a height of 160 mm, and aninternal diameter of 20 mm for 10 seconds at a sample length of 30 cmaccording to JIS L 1091 (1977), a flame remaining time and acarbonization length were obtained, and flame resistance was assessedfrom those values using the following criteria:

-   -   [Flame resistance excellent]: A flame remaining time is 10        seconds or shorter, and a carbonization length is 5 cm or less.    -   [Flame resistance good]: A flame remaining time is 10 seconds or        shorter, and a carbonization length is 10 cm or less.    -   [Presence of flame resistance]: A flame remaining time is 10        seconds or shorter, and a carbonization length is 15 cm or less.    -   [Worse]: A remaining time is more than 10 seconds, or a        carbonization length is more than 15 cm.        The measurement number n is 5, and the state in which the        corresponding number is most is defined as flame resistance of a        sample. When the assessment is not determined, n=5 assessment is        further added, and measurement is repeated until assessment is        determined.        Tensile Strength, Tensile Elastic Modulus and Tensile Elongation        of Single Fiber

In any case, a tensile test is performed according to JIS L1013 (1999).A single fiber having a length of 25 mm was adhered to a paper piecehaving a smooth and lustrous surface one by one at every 5 mm width, inthe state where both ends were mildly stretched with an adhesive so thata sample length became about 20 mm. A sample was attached to a gripperof a fiber tensile tester, the paper piece was cut near an uppergripper, and the sample was measured at a sample length of 20 mm, and atensile rate of 20 mm/min. The measurement number n was 50, and anaverage was defined as a tensile strength, a tensile elastic modulus andtensile elongation, respectively. In Examples, as a fiber tensiletester, Model 1125 manufactured by Instron was used.

Example 1

A dispersion in which 10.0 parts by weight of an acrylonitrilehomopolymer as a precursor polymer, 3.5 parts by weight ofmonoethanolamine as a cyclizing agent, 8.0 parts by weight oforthonitrotoluene as an oxidizing agent, and 3.0 parts by weight ofbenzoic acid as an acid were dispersed in 75.5 parts by weight ofdimethyl sulfoxide as an organic solvent was stirred at a temperature of150° C. for 8 hours, and cooled to a temperature of 30° C. to obtain adispersion in which a flame-resistant polymer was dispersed in dimethylsulfoxide. The average thickness of a film made by the method of“Tensile strength per unit cross-sectional area in water,” of theresulting dispersion containing a flame-resistant polymer was 141 μm,and the tensile strength per cross-sectional area was 3.15 MPa. Inaddition, the concentration of the flame-resistant polymer of theresulting dispersion containing a flame-resistant polymer was 12.1% byweight and, when the flame-resistant polymer isolated from thedispersion containing a flame-resistant polymer was analyzed by 13C-NMR,there was clearly a peak derived from the flame-resistant polymer whichwas not confirmed in polyacrylonitrile as a precursor polymer, anorganic solvent, or a modifier, at 160 to 180 ppm. In addition, whenanalyzed by IR, there was a clear peak at 1600 cm⁻¹.

When this dispersion containing a flame-resistant polymer was assessedby spinning by the method of “Assessment of yarn breaking at washing-I,”there was no (0 mg) single fiber floating or settling in a water bath,and assessment was excellent (⊚). In addition, single fiber breaking orclogging at a die orifice site was not entirely present. Then, when theassessment was performed by spinning by the method of “Assessment ofyarn breaking at washing-II,” there was 10 mg of a short fiber floatingor settling in a water bath, and assessment was excellent (⊚).Thereafter, an aminosilicone lubricant was imparted, and the yarn wasdried at a temperature of 220° C. for 3 minutes in a hot air circulatingfurnace. The specific gravity of the dried yarn was 1.30, and theelongation of the dried yarn was 3.0%. Further, the dried yarn wasstretched 1.5-fold and, at the same time, heat-treated at a temperatureof 300° C. for 3 minutes in a hot air circulating furnace to obtain aflame-resistant fiber bundle. The fineness of a single yarn in theresulting flame-resistant fiber bundle was 1.0 dtex, the strength was2.3 g/dtex, and the elongation was 18%. When the flame resistance wasassessed, the yarn became red without burning, and it was seen that theyarn has excellent flame resistance such as a carbonization length of 1cm. Further, the flame-resistant fiber bundle obtained from theflame-resistant polymer was pre-carbonized at a temperature of 300 to800° C. in the nitrogen atmosphere, and carbonization-treated at atemperature of 1400° C. in the nitrogen atmosphere to obtain a carbonfiber bundle. The strength of the resulting carbon fiber bundle was 3600MPa, the elastic modulus was 230 GPa, and the specific gravity was 1.78.

Example 2

An experiment was performed in the same manner as in Example 1 exceptthat 3.0 parts by weight of p-hydroxybenzoic acid as an acid was used.The average thickness of a film made by the method of “Tensile strengthper unit cross-sectional area in water,” of the resulting dispersioncontaining a flame-resistant polymer was 141 μm, and the tensilestrength per cross-sectional area was 2.86 MPa. During this, there wasneither single yarn breaking nor clogging at a die orifice site. Inaddition, the concentration of the flame-resistant polymer in thedispersion containing a flame-resistant polymer was 12.2% by weight and,when the flame-resistant polymer isolated from the dispersion containinga flame-resistant polymer was analyzed by 13C-NMR, there was clearly apeak derived from the flame-resistant polymer which is not confirmed inpolyacrylonitrile as a precursor polymer, an organic solvent, or amodifier, at 160 to 180 ppm. In addition, when analyzed by IR, there wasa clear peak at 1600 cm⁻¹. When this dispersion containing aflame-resistant polymer was assessed by spinning by the method of“Assessment of yarn breaking at washing-I,” there was 0 mg of singlefiber floating or settling in a water bath, and assessment was excellent(⊚). In addition, single fiber breaking or clogging at a die orificesite was not entirely present. Then, when the assessment was performedby spinning by the method of “Assessment of yarn breaking atwashing-II,” there was 16 mg of a short fiber floating or settling in awater bath, and assessment was good (◯). The specific gravity of thedried yarn obtained from this was 1.30, and the elongation of the driedyarn was 3.1%. In addition, the bundle strength of the flame-resistantfiber was 2.3 g/detx, and elongation was 17.5%. When the flameresistance of this fiber was assessed, the bundle became red withoutburning, and it was seen that it has excellent flame resistance such asa carbonization length of 1.5 cm. Further, the strength of the carbonfiber bundle was 3200 MPa, the elastic modulus was 220 GPa, and thespecific gravity was 1.74.

Example 3

An experiment was performed as in Example 1, except that 2.5 parts byweight of monoethanolamine as a cyclizing agent, 7.0 parts by weight oforthonitrotoluene as an oxidizing agent, 3.0 parts by weight ofp-hydroxybenzoic acid as an acid, and 77.5 parts by weight of dimethylsulfoxide as an organic solvent were used. The average thickness of afilm made by the method of “Tensile strength per unit cross-sectionalarea in water,” of the resulting dispersion containing a flame-resistantpolymer was 130 μm, and the tensile strength per cross-sectional areawas 2.46 MPa. During this, there was neither single yarn breaking norclogging at a dye orifice site. In addition, the concentration of theflame-resistant polymer in the dispersion containing a flame-resistantpolymer was 12.1% by weight and, when the flame-resistant polymerisolated from the dispersion containing a flame-resistant polymer wasanalyzed by 13C-NMR, there was clearly a peak derived from theflame-resistant polymer which was not confirmed in polyacrylonitrile asa precursor polymer, an organic solvent, or a modifier, at 160 to 180ppm. In addition, when analyzed by IR, there was a clear peak at 1600cm⁻¹. When this dispersion containing a flame-resistant polymer wasassessed by spinning by the method of “Assessment of yarn breaking atwashing-I,” there was 2 mg of single fibers floating or settling in awater bath, and assessment was excellent (⊚). In addition, single fiberbreaking or clogging at a die orifice site was not entirely present.Then, when the assessment was performed by spinning by the method of“Assessment of yarn breaking at washing-II,” there was 26 mg of shortfibers floating or settling in a water bath, and assessment was good(◯). The specific gravity of the dried yarn obtained from this was 1.31,and elongation of the dried yarn was 3.0%. In addition, the bundlestrength of the flame-resistant fiber was 2.2 g/detx, and elongation was18.0%. When the flame resistance of this fiber was assessed, the bundlebecame red without burning, and it was seen that it has excellent flameresistance such as a carbonization length of 1.0 cm. Further, thestrength of the carbon fiber bundle was 3250 MPa, the elastic moduluswas 235 GPa, and the specific gravity was 1.75.

Example 4

An experiment was performed in the same manner as in Example 1 exceptthat 5.0 parts by weight of benzenesulfonic acid as an acid was used.The average thickness of a film made by the method of “Tensile strengthper unit cross-sectional area in water,” of the resulting dispersioncontaining a flame-resistant polymer was 124 μm, and the tensilestrength per cross-sectional area was 1.19 MPa. In addition, aconcentration of the flame-resistant polymer in the dispersion of aflame-resistant polymer was 12.1% by weight and, when theflame-resistant polymer isolated from the dispersion containing aflame-resistant polymer was analyzed by 13C-NMR, there was clearly apeak derived from the flame-resistant polymer which was confirmed inpolyacrylonitrile as a precursor polymer, an organic solvent, or amodifier, at 160 to 180 ppm. In addition, when analyzed by IR, there wasa clear peak at 1600 cm⁻¹. When this dispersion containing aflame-resistant polymer was assessed by spinning by the method of“Assessment of yarn breaking at washing-I,” there was 18 mg of singlefibers floating or settling in a water bath, and assessment was good(◯). In addition, single fiber breaking or clogging at a die orificesite was not entirely present. Then, when assessment was performed byspinning by the method of “Assessment of yarn breaking at washing-II,”there was 45 mg of short fibers floating or settling in a water bath,and assessment was good (◯). The specific gravity of the dried yarnobtained from this was 1.32, and elongation of the dried yarn was 2.8%.In addition, the bundle strength of the flame-resistant fiber was 2.0g/detx, and elongation was 17.5%. When flame resistance of this fiberwas assessed, the bundle became red without burning, and it was seenthat it has excellent flame resistance such as a carbonization length of1.0 cm. Further, a strength of the carbon fiber bundle was 3300 MPa, anelastic modulus was 235 GPa, and a specific gravity was 1.74.

Example 5

An experiment was performed in the same manner as in Example 1 exceptthat 0.75 part by weight of terephthalic acid as an acid was used. Theaverage thickness of a film made by the method of “Tensile strength perunit cross-sectional area in water,” of the resulting dispersioncontaining a flame-resistant polymer was 137 μm, and the tensilestrength per cross-sectional area was 5.03 MPa. In addition, theconcentration of the flame-resistant polymer in the dispersion of theflame-resistant polymer was 12.1% by weight and, when theflame-resistant polymer isolated from the dispersion containing aflame-resistant polymer was analyzed by 13C-NMR, there was clearly apeak derived from the flame-resistant polymer which was confirmed inpolyacrylonitrile as a precursor polymer, an organic solvent, or amodifier, at 160 to 180 ppm. In addition, when analyzed by IR, there wasa clear peak at 1600 cm⁻¹. When this dispersion containing aflame-resistant polymer was spun by the methods of “Assessment of yarnbreaking at washing-I” and “Assessment of yarn breaking at washing-II,”a dry mass of a single fiber floating or settling in a water bath was 0mg in both methods, and assessment of both of them was excellent (⊚). Aspecific gravity of the dried yarn obtained from this was 1.34, andelongation of the dried yarn was 3.0%. In addition, the bundle strengthof the flame-resistant fiber was 2.5 g/detx, and elongation was 16.0%.When flame resistance of this fiber was assessed, the bundle became redwithout burning, and it was seen that it has excellent flame resistancesuch as a carbonization length of 1.0 cm. Further, a strength of thecarbon fiber bundle was 3800 MPa, an elastic modulus was 240 GPa, and aspecific gravity was 1.76.

Example 6

An experiment was performed in the same manner as in Example 1 exceptthat 0.75 part by weight of adipic acid as an acid was used. The averagethickness of a film made by the method of “Tensile strength per unitcross-sectional area in water,” of the resulting dispersion containing aflame-resistant polymer was 125 μm, and the tensile strength percross-sectional area was 3.19 MPa. In addition, a concentration of theflame-resistant polymer in the dispersion of the flame-resistant polymerwas 12.2% by weight and, when the flame-resistant polymer isolated fromthe dispersion containing a flame-resistant polymer was analyzed by13C-NMR, there was clearly a peak derived from the flame-resistantpolymer which was confirmed in polyacrylonitrile as a precursor polymer,an organic solvent, or a modifier, at 160 to 180 ppm. In addition, whenanalyzed by IR, there was a clear peak at 1600 cm⁻¹. When thisdispersion containing a flame-resistant polymer was assessed by spinningby the method of “Assessment of yarn breaking at washing-I,” there was 0mg of single fibers floating or settling in a water bath, and assessmentwas good (⊚). In addition, single fiber breaking or clogging at a dieorifice site was not entirely present. Then, when assessment wasperformed by spinning by the method of “Assessment of yarn breaking atwashing-II,” there was 8 mg of short fibers floating or settling in awater bath, and assessment was good (⊚). Further, a strength of thecarbon fiber bundle was 3210 MPa, an elastic modulus was 220 GPa, and aspecific gravity was 1.78.

Example 7

According to the same manner as that of Example 1 except that an acidwas not added, and 2.0 parts by weight of phthalic anhydride was added,an experiment was performed. The average thickness of a film made by themethod of “Tensile strength per unit cross-sectional area in water,” ofthe resulting dispersion containing a flame-resistant polymer was 136μm, and the tensile strength per cross-sectional area was 2.09 MPa. Inaddition, the concentration of the flame-resistant polymer in thedispersion containing a flame-resistant polymer was 12.1% by weight and,when the flame-resistant polymer isolated from the dispersion containinga flame-resistant polymer was analyzed by 13C-NMR, there was clearly apeak derived from the flame-resistant polymer which was not confirmed inpolyacrylonitrile as a precursor polymer, an organic solvent, or amodifier, at 160 to 180 ppm. In addition, when analyzed by IR, there wasa clear peak at 1600 cm⁻¹. When this dispersion containing aflame-resistant polymer was assessed by spinning by the method of“Assessment of yarn breaking at washing-I,” there was 2 mg of singlefibers floating or settling in a water bath, and assessment wasexcellent (⊚). In addition, single fiber breaking or clogging at a dyeorifice site was not entirely present. Then, when assessment wasperformed by spinning by the method of “Assessment of yarn breaking atwashing-II,” there was 16 mg of short fibers floating or settling in awater bath, and assessment was good (◯). The strength of the carbonfiber bundle obtained from this was 3200 MPa, the elastic modulus was230 GPa, and the specific gravity was 1.71.

Example 8

According to the same manner as that of Example 1 except that an acidwas not added, and 3.0 parts by weight of benzoyl chloride was added, anexperiment was performed. The average thickness of a film made by themethod of “Tensile strength per unit cross-sectional area in water,” ofthe resulting dispersion containing a flame-resistant polymer was 140μm, and the tensile strength per cross-sectional area was 2.79 MPa. Inaddition, the concentration of the flame-resistant polymer in thedispersion containing a flame-resistant polymer was 12.3% by weight and,when the flame-resistant polymer isolated from the dispersion containinga flame-resistant polymer was analyzed by 13C-NMR, there was clearly apeak derived from the flame-resistant polymer which was not confirmed inpolyacrylonitrile as a precursor polymer, an organic solvent, or amodifier, at 160 to 180 ppm. In addition, when analyzed by IR, there wasa clear peak at 1600 cm⁻¹. When this dispersion containing aflame-resistant polymer was assessed by spinning by the method of“Assessment of yarn breaking at washing-I,” there was 3 mg of singlefibers floating or settling in a water bath, and assessment wasexcellent (⊚). In addition, single fiber breaking or clogging at a dyeorifice site was not entirely present. Then, when assessment wasperformed by spinning by the method of “Assessment of yarn breaking atwashing-II,” there was 18 mg of short fibers floating or settling in awater bath, and assessment was good (◯). The strength of the carbonfiber bundle obtained from this was 3150 MPa, the elastic modulus was210 GPa, and the specific gravity was 1.73.

Example 9

An experiment was performed in the same manner as in Example 1 exceptthat 0.1 part by weight of taurine as an acid was used. The averagethickness of a film made by the method of “Tensile strength per unitcross-sectional area in water,” of the resulting dispersion containing aflame-resistant polymer was 125 μm, and the tensile strength percross-sectional area was 4.93 MPa. In addition, the concentration of theflame-resistant polymer in the dispersion of a flame-resistant polymerwas 12.4% by weight and, when the flame-resistant polymer isolated fromthe dispersion containing a flame-resistant polymer was analyzed by13C-NMR, there was clearly a peak derived from the flame-resistantpolymer which was confirmed in polyacrylonitrile as a precursor polymer,an organic solvent, or a modifier, at 160 to 180 ppm. In addition, whenanalyzed by IR, there was a clear peak at 1600 cm⁻¹. When thisdispersion containing a flame-resistant polymer was assessed by spinningby the method of “Assessment of yarn breaking at washing-I,” there was 0mg of single fibers floating or settling in a water bath, and assessmentwas good (⊚). In addition, single fiber breaking or clogging at a dieorifice site was not entirely present. Then, when assessment wasperformed by spinning by the method of “Assessment of yarn breaking atwashing-II,” there was 4 mg of short fibers floating or settling in awater bath, and assessment was good (⊚). Thereafter, an aminosiliconelubricant was imparted, and the yarn was dried at a temperature of 220°C. for 4 minutes in a hot air circulating furnace. The specific gravityof the dried yarn was 1.32, and the elongation of the dried yarn was3.1%. Further, the dried yarn was stretched 1.5-fold and, at the sametime, heat-treated at a temperature of 300° C. for 3 minutes in a hotair circulating furnace to obtain a flame-resistant fiber bundle. Thefineness of a single yarn in the resulting flame-resistant fiber bundlewas 1.0 dtex, the strength was 2.4 g/dtex, and the elongation was 15%.In addition, when flame resistance was assessed, the bundle became redwithout burning, and it was seen that the yarn has excellent flameresistance such as a carbonization length of 1 cm. Further, this wascarbonized by the same method as that of Example 1, the strength of theresulting carbon fiber bundle was 3330 MPa, and the elastic modulus was298 GPa, and the specific gravity was 1.78.

Example 10

An experiment was performed as in Example 1 except that 0.5 parts byweight of sulfanilic acid as an acid was used. The average thickness ofa film made by the method of “Tensile strength per unit cross-sectionalarea in water,” of the resulting dispersion containing a flame-resistantpolymer was 127 μm, and the tensile strength per cross-sectional areawas 5.08 MPa. In addition, the concentration of the flame-resistantpolymer in the dispersion of the flame-resistant polymer was 12.6% byweight and, when the flame-resistant polymer isolated from thedispersion containing a flame-resistant polymer was analyzed by 13C-NMR,there was clearly a peak derived from the flame-resistant polymer whichwas confirmed in polyacrylonitrile as a precursor polymer, an organicsolvent, or a modifier, at 160 to 180 ppm. In addition, when analyzed byIR, there was a clear peak at 1600 cm⁻¹. When this dispersion containinga flame-resistant polymer was assessed by spinning by the method of“Assessment of yarn breaking at washing-I,” there was 0 mg of singlefibers floating or settling in a water bath, and assessment was good(⊚). In addition, single fiber breaking or clogging at a die orificesite was not entirely present. Then, when assessment was performed byspinning by the method of “Assessment of yarn breaking at washing-II,”there was 0 mg of short fibers floating or settling in a water bath, andassessment was good (⊚). Further, the specific gravity of the dried yarnobtained this was 1.30, and the elongation of the dried yarn was 3.2%.In addition, the bundle strength of the flame-resistant fiber was 2.5g/detx, and the elongation was 18.0%. When flame resistance of thisfiber was assessed, the bundle became red without burning, and it wasseen that it has excellent flame resistance such as a carbonizationlength of 1.0 cm. Further, the strength of the carbon fiber bundle was3520 MPa, the elastic modulus was 267 GPa, and the specific gravity was1.77.

Example 11

According to the same manner as that of Example 1 except that 2.0 partsby weigh of monoethanolamine as a cyclizing agent, 1.5 parts by weightof nitrobenzene as an oxidizing agent, and 0.3 part by weight of taurineas an acid were added, an experiment was performed. The averagethickness of a film made by the method of “Tensile strength per unitcross-sectional area in water,” of the resulting dispersion containing aflame-resistant polymer was 125 μm, and the tensile strength percross-sectional area was 5.91 MPa. In addition, the concentration of theflame-resistant polymer in the dispersion of the flame-resistant polymerwas 12.3% by weight and, when the flame-resistant polymer isolated fromthe dispersion containing a flame-resistant polymer was, there was aclear peak at 1600 cm⁻¹. When this dispersion containing aflame-resistant polymer was assessed by spinning by the method of“Assessment of yarn breaking at washing-I,” there was 0 mg of singlefibers floating or settling in a water bath, and assessment wasexcellent (⊚). In addition, single fiber breaking or clogging at a dieorifice site was not entirely present. Then, when the assessment wasperformed by spinning by the method of “Assessment of yarn breaking atwashing-II,” there was 0 mg of short fibers floating or settling in awater bath, and assessment was excellent (⊚). Further, the specificgravity of the dried yarn obtained this was 1.32, and the elongation ofthe dried yarn was 3.0%. In addition, the bundle strength of theflame-resistant fiber was 2.3 g/detx, and the elongation was 19.0%. Whenflame resistance of this fiber was assessed, the bundle became redwithout burning, and it was seen that it has excellent flame resistancesuch as a carbonization length of 3.0 cm. Further, the strength of thecarbon fiber bundle was 3100 MPa, the elastic modulus was 240 GPa, andthe specific gravity was 1.79.

Example 12

According to the same manner as that of Example 1 except that 2.5 partsby weigh of monoethanolamine as a cyclizing agent, 1.2 parts by weightof nitrobenzene as an oxidizing agent, and 0.2 part by weight of taurineas an acid were added, an experiment was performed. The averagethickness of a film made by the method of “Tensile strength per unitcross-sectional area in water,” of the resulting dispersion containing aflame-resistant polymer was 135 μm, and the tensile strength percross-sectional area was 4.00 MPa. In addition, the concentration of theflame-resistant polymer in the dispersion of a flame-resistant polymerwas 12.2% by weight and, when the flame-resistant polymer isolated fromthe dispersion containing a flame-resistant polymer was, there was aclear peak at 1600 cm⁻¹. When this dispersion containing aflame-resistant polymer was assessed by spinning by the method of“Assessment of yarn breaking at washing-I,” there was 1 mg of singlefibers floating or settling in a water bath, and assessment wasexcellent (⊚). In addition, single fiber breaking or clogging at a dieorifice site was not entirely present. Then, when the assessment wasperformed by spinning by the method of “Assessment of yarn breaking atwashing-II,” there was 5 mg of short fibers floating or settling in awater bath, and assessment was excellent (⊚). Further, the specificgravity of the dried yarn obtained this was 1.31, and the elongation ofthe dried yarn was 3.1%. In addition, the bundle strength of theflame-resistant fiber was 2.2 g/detx, and the elongation was 19.0%. Whenflame resistance of this fiber was assessed, the bundle became redwithout burning, and it was seen that it has excellent flame resistancesuch as a carbonization length of 4.0 cm. Further, the strength of thecarbon fiber bundle was 3020 MPa, the elastic modulus was 250 GPa, andthe specific gravity was 1.78.

Example 13

An experiment was performed as in Example 1 except that 0.75 part byweight of phthalic acid as an acid was used. The average thickness of afilm made by the method of “Tensile strength per unit cross-sectionalarea in water,” of the resulting dispersion containing a flame-resistantpolymer was 145 μm, and the tensile strength per cross-sectional areawas 4.96 MPa. In addition, the concentration of the flame-resistantpolymer in the dispersion of a flame-resistant polymer was 12.4% byweight and, when the flame-resistant polymer isolated from thedispersion containing a flame-resistant polymer was analyzed by 13C-NMR,there was clearly a peak derived from the flame-resistant polymer whichwas confirmed in polyacrylonitrile as a precursor polymer, an organicsolvent, or a modifier, at 160 to 180 ppm. In addition, when analyzed byIR, there was a clear peak at 1600 cm⁻¹. When this dispersion containinga flame-resistant polymer was assessed by spinning by the method of“Assessment of yarn breaking at washing-I,” there was 1 mg of singlefibers floating or settling in a water bath, and assessment was good(⊚). In addition, single fiber breaking or clogging at a die orificesite was not entirely present. Then, when assessment was performed byspinning by the method of “Assessment of yarn breaking at washing-II,”there was 3 mg of short fibers floating or settling in a water bath, andassessment was good (⊚). The specific gravity of the dried yarn obtainedthis was 1.30, and the elongation of the dried yarn was 3.0%. Inaddition, the bundle strength of the flame-resistant fiber was 2.2g/detx, and the elongation was 18.5%. When flame resistance of thisfiber was assessed, the bundle became red without burning, and it wasseen that it has excellent flame resistance such as a carbonizationlength of 1.5 cm. Further, the strength of the carbon fiber bundle was3250 MPa, the elastic modulus was 235 GPa, and the specific gravity was1.76.

Comparative Example 1

A solution in which 10 parts by weight of an acrylonitrile homopolymeras a precursor polymer, 3.5 parts by weight of monoethanolamine as acyclizing agent, and 8.0 parts by weight of orthonitrotoluene as anoxidizing agent were dissolved in 74.0 parts by weight of dimethylsulfoxide as an organic solvent was stirred at a temperature of 150° C.for 8 hours, and cooled to a temperature of 30° C. to obtain adispersion in which the flame-resistant polymer was dispersed. Theaverage thickness of a film made by the method of “Tensile strength wereunit-sectional area in water” of the resulting dispersion containing aflame-resistant polymer was 143 μm, and the tensile strength percross-sectional area was 0.3 MPa. In addition, the concentration of theflame-resistant polymer in the dispersion of a flame-resistant polymerwas 12.1% by weight and, when the flame-resistant polymer isolated fromthe dispersion containing a flame-resistant polymer was analyzed by13C-NMR, there was clearly a peak derived from the flame-resistantpolymer which was not confirmed in polyacrylonitrile as a precursorpolymer, an organic solvent, or a modifier, at 160 to 180 ppm. Inaddition, when analyzed by IR, there was a clear peak at 1600 cm⁻¹. Whenthis dispersion containing a flame-resistant polymer was spun by themethod of “Assessment of yarn breaking at washing-I,” the dry mass ofsingle fibers floating or settling in the water bath was 68 mg, andassessment was worse (x). The specific gravity of the dried yarnobtained from this was 1.28, and elongation of the dried yarn was 2.1%.In addition, the bundle strength of the flame-resistant fiber was 1.4g/detx, and the elongation was 13.0%. When flame resistant of this fiberwas assessed, it became red without burning, and it was seen that it hasexcellent flame resistance such as a carbonization length of 1.5 cm.Further, the strength of the carbon fiber bundle was 1500 MPa, theelastic modulus was 145 GPa, and the specific gravity was 1.72.

Thus, when the dispersion in which an acrylonitrile polymer wasdispersed in a polar solvent was heat-treated under the condition of theabsence of all of an acid, an acid anhydride and an acid chloride,sufficient flame resistance can be imparted to an acrylonitrile polymer,but when treated under the condition of the absence of all of an acid,an acid anhydride, and an acid chloride, a sufficient strength cannot beobtained upon shaping of the flame-resistant polymer into a yarn, yarnbreaking occurs frequently at steps, and it is clear that physicalproperties of the resulting flame-resistant yarn and carbon fiber areremarkably reduced.

TABLE 1 Example 1 2 3 4 5 6 7 Raw Precursor Acrylonitrile Part 10.0 10.010.0 10.0 10.0 10.0 10.0 material polymer homopolymer Organic DimethylPart 75.5 75.5 77.5 75.5 75.5 75.5 75.5 solvent sulfoxide CyclizingMonoethanolamine Part 3.5 3.5 2.5 3.5 3.5 3.5 3.5 agent OxidizingOrthonitro- Part 8.0 8.0 7.0 8.0 8.0 8.0 8.0 agent toluene Nitro- Part —— — — — — — benzene Orthonitro- Part — — — — — — — phenol Acid BenzoicPart 3.0 — — — — — — (mono- acid carboxylic p-hydroxy- Part — 3.0 3.0 —— — — acid) benzoic Acid acid (Dicarboxylic Phthalic Part — — — — — — —acid) acid Terephthalic Part — — — — 0.75 — — acid Adipic Part — — — — —0.75 — acid Acid Benzene- Part — — — 5.0 — — — (sulfonic sulfonic acid)acid Acid Taurine Part — — — — — — — (amino- Sulfanilic Part — — — — — —— sulfonic acid acid) Acid Phthalic Part — — — — — — 2.0 anhydrideanhydride Acid Benzoyl Part — — — — — — — chloride chloride Flame-Average μm 141 141 130 124 137 125 136 resistant thickness of filmpolymer/ Tensile strength Npa 3.15 2.86 2.46 1.19 5.03 3.19 2.09properties per cross-sectional area Concentration of % 12.1 12.2 12.112.1 12.1 12.2 12.1 flame-resistant polymer 13C-NMR Peak at 160Presence/ Presence Presence Presence Presence Presence Presence Presenceto 180 ppm Absence IR Peak at 1600 cm−1 Presence/ Presence PresencePresence Presence Presence Presence Presence Absence Assessment of yarn⊚/◯/X ⊚ ⊚ ⊚ ◯ ⊚ ⊚ ⊚ breaking at washing 1 Assessment of yarn ⊚/◯/X ⊚ ◯ ◯◯ ⊚ ⊚ ◯ breaking at washing 2 Specific gravity — 1.30 1.30 1.31 1.321.34 — — of dried yarn Elongation % 3.0 3.1 3.0 2.8 3.0 — — of driedyarn Flame-resistant gf/dtex 2.3 2.3 2.2 2.0 2.5 — — fiber bundlestrength Elongation % 18 17.5 18.0 17.5 16.0 — — Flame Carbonization cm1 1.5 1.0 1.0 1.0 — — resistance length Carbon Strength Mpa 3600 32003250 3300 3800 3210 3200 fiber Elastic Gpa 230 220 235 235 240 220 230propeerties modulus Specific — 1.78 1.74 1.75 1.74 1.76 1.78 1.71gravity Comparative Example Example 8 9 10 11 12 13 1 Raw PrecursorAcrylonitrile Part 10.0 10.0 10.0 10.0 10.0 10.0 10.0 material polymerhomopolymer Organic Dimethyl Part 75.5 75.5 75.5 75.5 75.5 75.5 74.0solvent sulfoxide Cyclizing Monoethanolamine Part 3.5 3.5 3.5 2.0 2.53.5 3.5 agent Oxidizing Orthonitro- Part 8.0 8.0 8.0 — — 8.0 8.0 agenttoluene Nitro- Part — — — 1.5 — — — benzene Orthonitro- Part — — — — 1.2— — phenol Acid Benzoic Part — — — — — — — (mono- acid carboxylicp-hydroxy- Part — — — — — — — acid) benzoic Acid acid (DicarboxylicPhthalic Part — — — — — 0.75 — acid) acid Terephthalic Part — — — — — —— acid Adipic Part — — — — — — — acid Acid Benzene- Part — — — — — — —(sulfonic sulfonic acid) acid Acid Taurine Part — 0.1 — 0.3 0.2 — —(amino- Sulfanilic Part — — 0.5 — — — — sulfonic acid acid) AcidPhthalic Part — — — — — — — anhydride anhydride Acid Benzoyl Part 3.0 —— — — — — chloride chloride Flame- Average μm 140 125 127 125 135 145143 resistant thickness of film polymer/ Tensile strength Npa 2.79 4.935.08 5.91 4.00 4.96 0.30 properties per cross-sectional areaConcentration of % 12.3 12.4 12.6 12.3 12.2 12.4 12.1 flame-resistantpolymer 13C-NMR Peak at 160 Presence/ Presence Presence PresencePresence Presence Presence Presence to 180 ppm Absence IR Peak at 1600cm−1 Presence/ Presence Presence Presence Presence Presence PresencePresence Absence Assessment of yarn ⊚/◯/X ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ X breaking atwashing 1 Assessment of yarn ⊚/◯/X ◯ ⊚ ⊚ ⊚ ⊚ ⊚ X breaking at washing 2Specific gravity — — 1.32 1.30 1.32 1.31 1.30 1.28 of dried yarnElongation % — 3.1 3.2 3.0 3.1 3.0 2.1 of dried yarn Flame-resistantgf/dtex — 2.4 2.5 2.3 2.2 2.2 1.4 fiber bundle strength Elongation % —15 18.0 19.0 19.0 18.5 13.0 Flame Carbonization cm — 1 1.0 3.0 4.0 1.51.5 resistance length Carbon Strength Mpa 3150 3330 3520 3100 3020 32501500 fiber Elastic Gpa 210 298 267 240 250 235 145 propeerties modulusSpecific — 1.73 1.78 1.77 1.79 1.78 1.76 1.72 gravity

INDUSTRIAL APPLICABILITY

The dispersion containing a flame-resistant polymer has remarkably goodrelease from an ejection port upon shaping it. Thus, in the dispersioncontaining a flame-resistant polymer, particularly, since release froman ejection die orifice site becomes good upon shaping into a yarn, itbecomes possible to suppress single yarn breaking and adhesion at theejection die orifice site and, further, since a shaped article having ahigh physical strength at coagulation is obtained, damage of the shapedarticle is considerably reduced in a step of removing a dispersingmedium remaining in the shaped article, that is, a washing stage, a steprate can be improved, being useful.

The invention claimed is:
 1. A dispersion comprising 1) aflame-resistant polymer obtained by heat-treating an acrylonitrilepolymer as a precursor polymer dispersed in 2) a polar organic solventin the presence of at least an acid, an acid anhydride or an acidchloride and 3) an oxidizing agent, wherein an in-water tensile strengthper unit cross-sectional area of the flame-resistant polymer is 1.0 MPaor more and 6.5 MPa or less, a total additional amount of the acid is0.05 part by weight to 5.0 parts by weight based on 10.0 parts by weightof the acrylonitrile polymer, and wherein the acid is a monocarboxylicacid selected from the group consisting of benzoic acid, hydroxybenzoicacid, methylbenzoic acid and aminobenzoic acid, a dicarboxylic acidselected from the group consisting of phthalic acid, isophthalic acidand terephthalic acid, or an aminosulfonic acid which is taurine orsulfanilic acid.
 2. A flame-resistant fiber comprising a shapeddispersion, wherein the dispersion is the dispersion containing aflame-resistant polymer of claim
 1. 3. A carbon fiber comprising acarbonized flame-resistant fiber, wherein the flame-resistant fiber isthe flame-resistant fiber of claim
 2. 4. The dispersion according toclaim 1, further comprising a cyclizing agent.